function slowStep(obj, target, fn) {
            clearInterval(obj.timer);
            obj.timer = setInterval(function () {
                let divL = div.offsetLeft;
                let step = (target - divL) / 10;
                step = step > 0 ? Math.ceil(step) : Math.floor(step);
                if (divL === target) {
                    clearInterval(obj.timer);
                    if (fn) {
                        fn();
                    }
                }
                div.style.left = divL + step + 'px';
            }, 30)
        }